Benzofuroxans spectra

Further benzofuroxan spectra are reported by Gaughran, Picard, and Kaufman, who compare them with benzofurazans, by Boyer et al., who find similarities with furoxans and nitroso compounds, and by others. Hexanitrosobenzene was shown by IR and Raman spectroscopy to exist in the benzotrifuroxan structure. ... 

No systematic investigation into the vibrations of the benzofuroxan molecule has been reported. Infrared data are available for a number of compounds, however. Boyer et al in 1963 listed four bands in the benzofuroxan spectrum at 1630, 1600, 1645, and 1500 cm . It is the present authors experience that four strong bands of comparable intensities at or near the frequencies quoted commonly occur in the spectra of substituted benzofuroxans, and are very useful for diagnostic purposes. One or more bands may be weak or absent, however for 2,3-pyridofuroxan (4-azabenzofuroxan) only two bands are reported in this region. 

Proton resonance techniques provided the hrst clear-cut evidence for the unsymmetrical structure of benzofuroxans and for their tautomerism. The unsymmetrical (ABCD) spectrum observed at low temperature (-40 °C) becomes well-resolved and symmetrical (A2B2) above... 

The 170 NMR spectrum of dimethylfuroxan consists of two distinct peaks at So-460 and -350 p.p.m. from H20 the former can be assigned to 0(1) by comparison with dimethylfurazan (So -475 p.p.m.) (61HCA865). Dynamic resonance effects are observed for benzofuroxan (62HCA504). 

Although the ultraviolet spectrum of benzofuroxan undergoes an extensive, and reversible, change on solution in fairly concentrated sulfuric acid, suggesting that protonation is occurring, the site of proton attachment is not known. Benzofuroxans behave approximately as Hammett bases (Gr. (logio[BH+] — logio [B])/Hq= 1), with pK s —8.3+ 0.1 (unsubst.), —8.4+ 0.1 (4-Me), —8.2+ 0.1 (5-Me) (cf. — 8.4 + 0.1 for benzofurazan). C-Protonation (as 35) would probably require the protonation to follow a steeper acidity function (cf. azulenes ), and therefore N- (36) or 0- (37) protonation is in-... 

The ortho proton-proton coupling constants in benzofuroxan show the expected alternation in magnitude, following the bond orders between the carbon atoms.90,98,99 Substituent effects on coupling constants have been correlated in a series ofbenzo-fused heterocycles, including benzofuroxan.109 The proton resonance spectrum of benzofuroxan in a nematic solvent has been published (somewhat obscurely).110... 

While the wide spectrum of biological activities for compounds containing the furoxan or benzofuroxan heterocycle were reported over three decades ago (Ghosh... 

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